Conventionally, calcium carbonate has been incorporated at a high concentration for use of plastisol in which a vinyl chloride resin or an acrylic resin and a plasticizer are mixed, and in the field of a sealant in which a urethane or a silicone resin, a polysulfide resin, and the like, are mixed. On the other hand, among synthetic resins, in the field in which a processing temperature is high, for example, a polyester resin typically such as a polyethylene terephthalate (PET), an engineering plastic typically such as a polyamide (PA), a polycarbonate (PC), and a polyphenylene sulfide (PPS), calcium carbonate has previously been incorporated in a very small amount for the purpose of a light diffusing material, an anti-blocking material, and the like.
For example, there has been proposed a method of adding calcium carbonate whose particle size has been adjusted as a micropore forming agent together with a non-compatible resin into a PET resin, and forming the mixture into a stretched film (sheet) (Patent Literature 1), a method of adding inorganic fine particles such as barium sulfate particles into a PET resin, and forming the mixture into a stretched film (sheet) (Patent Literature 2), and the like. A porous white PET film produced by a method of forming porous voids at an interface between a PET resin and a micropore forming agent has been put into practical use in a wide variety of fields such as a synthetic paper, (prepaid) cards, labels, optical reflecting films (sheets), and the like. Among them, for example, in the case of a light reflecting film utilized for liquid crystal TV, high image quality, wide screen, and low cost of liquid crystal TV are required.